1. Technical Field
The following description relates to one or more techniques for communicating with other devices via a network by using a secret key and an electronic certificate including information on a public key corresponding to the secret key.
2. Related Art
Conventionally, there is known a communication technology using an electronic certificate (for example, see Japanese Patent Provisional Publication No. 2004-302835). In addition, an SSL (Secure Socket Layer) communication technology is known as the communication technology using the electric certificate. In order to attain the SSL communication, it is required to generate a pair of a secret key and a public key and to request a CA (Certificate Authority) to issue the electric certificate regarding the public key prior to performing the communication. Then, the generated secret key and electronic certificate are installed into a server device with which the SSL communication is to be performed.
When an initial signal for an SSL handshake has been transmitted from a client device to the server device into which the secret key and electronic certificate are installed as aforementioned, the server device sends the electronic certificate to the client device.
When the electronic certificate has been received from the server device, the client device judges whether the electronic certificate as received is proper. For instance, the client device evaluates a digital signature of the electronic certificate as received based on the digital signature and the CA certificate, and judges whether the electronic certificate has been falsified. Further, based on validity period information included in the electronic certificate, it is judged whether the electronic certificate is expired.
Additionally, in order to judge whether the electronic certificate is revoked, the client device acquires a CRL (Certificate Revocation List) managed by a management device such as the CA from the management device. Then, the client device checks the electronic certificate against the acquired CRL to judge whether the electronic certificate acquired from the server device is revoked.
When the electronic certificate is judged to be valid, the client device trusts the server device and performs following procedures. Specifically, encrypted communication between the server device and the client device is performed using the secret key and public key, so as to arrange a session key (common key). Thereafter, the encrypted communication using the session key is performed. In the meantime, when the electronic certificate is not judged to be valid based on the CRL, the following procedures are not performed and the communication is broken to prevent masquerading.
Meanwhile, in order to attain high-security communication using the SSL communication technology, it is required to always reflect the latest information in the aforementioned CRL. This is because even though the electronic certificate is not expired, when the client device trusts the server device only based on the electronic certificate, a communication security problem might be caused.
For example, the secret key and electronic certificate may be deleted from a memory area of the server device due to initialization of the server device, and may not be used at the server device side. In addition, an administrator of the server device may delete the secret key and electronic certificate that have been used so far in order to prevent the secret key from being stolen and abused, and may introduce a new secret key and a new electronic certificate into the server device, even though the electronic certificate is not expired.
Here, assuming the secret key and electronic certificate have already been stolen before the secret key and electronic certificate are deleted from the server device, a false server device might masquerade as the proper server device by using the secret key and electronic certificate that had been used by the proper server device until they were stolen.
In this case, when the electronic certificate is not registered in the CRL, the client device may judge that an electronic certificate transmitted from the false server device is proper, and may continue the communication.
Namely, when there is not registered in the CRL information on revocation of the electronic certificates that is not used by the proper server device any more, the communication security is significantly reduced. However, in a conventional system, the management device that manages the CRL cannot detect the secret key or electronic certificate that has been deleted from each server device. Therefore, a large amount of labor is required for registering, into the CRL, information on the electronic certificates that are not used by the server device any more due to initializing the server device or updating the secret key, since large portion of the operation for registering the information into the CRL is manually performed.